Fault inversion contributes to ground deformation above inflating igneous sills

Space for magma is commonly generated by uplift of the overburden and free surface. If this deformation is elastic, we can invert the shape and kinematics of ground movement to model the geometry and dynamics of underlying intrusions. However, magma emplacement can be spatially accommodated by viscoelastic and/or plastic host rock deformation, although few studies have quantified the contributions of these processes. We restore ground deformation above a sill, imaged in 3D seismic reflection data, and show that: (i) where uplift equalled sill thickness, host rock bending accommodated intrusion; but (ii) where sill thickness exceeded uplift, normal fault inversion and overburden compaction generated space for intrusion. Our results support work showing intrusion-induced ground deformation may be restricted if multiple deformation processes accompany emplacement. We also demonstrate intrusion-induced uplift can drive fault inversion, meaning the present pattern of displacement on the faults surface may not reflect its tectonic growth history.